Carburetor having an automatic choke

ABSTRACT

A CARBURETOR, HAVING A CHOKE VALVE WITH THERMOSTATIC MEANS ADAPTED TO URGE THE COKE VALVE IN THE CLOSING DIRECTION WHEN COLD, IS PROVIDED WITH PRESSURE RESPONSIVE MEANS WHICH COMMUNICATES WITH A SOURCE OF ENGINE VACUUM FOR MOVING THE CHOKE VALVE IN A DIRECTION OPPOSITE TO THAT OF THE THERMOSTATIC MEANS UPON ENGINE STARTING, THE DEGREE OF EFFECTIVE COMMUNICATION BETWEEN THE PRESSURE RESPONSIVE MEANS THE SOURCE OF ENGINE VACUUM IS CONTROLLED IN ACCORDANCE WITH THE POSITION OF THE CARBURETOR THROTTLE VALVE IS ORDER THAT THE PRESSURE RESPONSIVE MEANS WILL BE EFFECTIVE FOR MOVING THE CHOKE VALVE TO A FIRST PARTLY OPENED POSITION WHEN THE THROTTLE VALVE IS IN THE NOMINALLY CLOSED POSITION AND TO A VARIABLE SECOND MORE FULLY OPENED POSITION WHEN THE THROTTLE VALVE IS MOVED TO A PART THROTTLE POSITION.

Sept. 21, 1971 R. D. MITCHELL CARBURETOR HAVING AN AUTOMATIC CHOKE FiledApril 21, 1969 52 ROBE/QTQM/Tf/ffll I N VENTOR.

United States Patent O 3,606,983 CARBURETOR HAVING AN AUTOMATIC CHOKERobert D. Mitchell, Madison Heights, Mich., assignor to HolleyCarburetor Company, Warren, Mich. Filed Apr. 21, 1969, Ser. No. 817,636Int. Cl. F02m 1/08 US. Cl. 261-39 12 Claims ABSTRACT OF THE DISCLOSURE Acarburetor, having a choke valve with thermostatic means adapted to urgethe choke valve in the closing direction when cold, is provided withpressure responsive means which communicates with a source of enginevacuum for moving the choke valve in a direction opposite to that of thethermostatic means upon engine starting; the degree of effectivecommunication between the pressure responsive means and the source ofengine vacuum is controlled in accordance With the position of thecarburetor throttle valve in order that the pressure responsive meanswill be effective for moving the choke valve to a first partly openedposition when the throttle valve is in its nominally closed position andto a variable second more fully opened position when the throttle valveis moved to a part throttle position.

BACKGROUND OF .THE INVENTION Heretofore, automatic choke mechanisms haveemployed either a diaphragm assembly or a pressure responsive piston incommunication with a source of engine or intake manifold vacuum formoving the choke valve, against the resisting force of a thermostattending to close the choke valve, to a partially open position, oftenreferred to as the qualifying position, after a cold or relatively coldengine has been started. A stepped fast idle cam positioned by chokevalve position then controlled idle throttle position.

It has also become accepted practice, in the prior art, to make suchpressure responsive diaphragms or pistons of the stopped type; that iswith either the stopped diaphragm or piston the initial qualifyingposition of the choke valve is determined by a positive mechanical stopwhich precludes any further movement of such diaphragm or piston in thechoke opening direction.

However, one disadvantage of the prior art arrangements, including thestopped type of diaphragm or piston employed by the prior art, is thatthere is no control or modulation of the choke position when the engineoperating conditions are changed from cold fast idle to cold enginedrive-away. Another disadvantage is that prior art choke systems resultin a single fixed qualifying choke valve position for the higher airflow steps on the fast idle cam.

That is, it is generally well known that a cold engine requires acombustible mixture which is of a richer fuelair ratio during cold idleengine operation in order to sustain engine operation and the initialchoke opening is selected in order to achieve such a richer mixture.However, upon undergoing cold drive-away conditions, at which higherengine speeds are also experienced, that initial opening of the chokevalve usually results in an overly rich fuel-air ratio. This in turnresults in the emission of unburned hydrocarbons, a reduction in overallfuel economy and often rough or sporadic engine operation.

The invention as herein disclosed and described is directly concernedwith the solution of the above as well as other problems.

"Ice

SUMMARY OF THE INVENTION According to the invention, a carburetor for aninter- .nal combustion engine comprises a choke valve, a throtpressureresponsive means being effective to move said choke valve to a firstpartly open position when said engine starts and the throttle valve isin its cold or fast idle (closed) position, said pressure responsivemeans also being effective to move said choke valve to a variable secondpartly open position more nearly fully open'ed than said first partlyopen position when said throttle valve is moved from its above-definedidle or closed position toward a part-throttle position.

Accordingly, a general object of the invention is to provide in acarburetor having a choke valve, means for positioning the choke valvein a first partly opened position when the throttle valve is closed andfor also positioning the choke valve in a variable second partly openedposition more fully opened than said first partly opened position whenthe throttle valve is moved away from its said closed position to anyhigher air flow position.

Other more specific objects and advantages of the invention will becomeapparent when reference is made to the following detailed descriptionand accompanying drawings.

DESCRIPTION OF THE DRAWINGS In the drawings, wherein certain details maybe omitted from one or more views for purposes of clarity:

BIG. 1 is a side elevational view of a carburetor, with portions thereofbroken away and in cross-section, constructed in accordance with theteachings of the invention.

FIG. 2 is an enlarged fragmentary view of a portion of the carburetor ofFIG. 1 sectioned axially through a cooperating pressure responsive chokeactuating means constructed in accordance with the teachings of theinvention;

FIG. 3 is a fragmentary cross-sectional view, similar to FIG. 2, but ofa second embodiment of the invention; and

FIG. 4 is an enlarged fragmentary portion of FIG. 1 illustrating ingreater detail certain of the elements shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in greater detailto the drawings, FIG. 1 illustrates a carburetor 10, constructed inaccordance with the invention, as comprising a carburetor body 12 formedto provide an induction passage 14 having the usual venturi restriction16 and a throttle valve 18, Within the induction passage downstream ofthe venturi 16, pivotally mounted on manually positionable throttleshaft 20. The entire carburetor assembly is suitably secured atop anengine intake manifold 22.

The throttle valve is opened, against the force of a spring 24 urging itclosed, in the usual manner as by means of suitable linkage 26 connectedbetween the throttle lever 28 and the operators foot pedal (not shown).As is customary, closure of the throttle 18 may be limited by anadjustable stop screw 30 adapted to be ro tated with the throttle valveand engageable with one of a plurality of cam-like steps (not shown)formed on a fast idle cam (fragmentarily illustrated at 32) which ispositioned generally by the choke mechanism 34 as through a lost motionlinkage member 36.

The choke mechanism 34 comprises a choke valve 38 mounted on a shaft 40for pivotal rotation within the induction passage means 14 upstream ofthe venturi 16. As is often the case, the choke valve 38 may beunbalanced to open by gravity and in response to airflow through theinduction passage. In such case the force of the air tending to open thechoke valve 38 is opposed by the coiled thermostatic spring 42, whichmay be mounted on the engine exhaust manifold 44 and operativelypivotally connected to a choke lever 46, which is secured to choke shaft40 for rotation therewith, by a linkage 48. The opposing force of thethermostat is at a maximum when the engine is cold and is progressive-1y relaxed as the engine warms up. The choke lever 46 is, in turn,operatively connected to the fast idle cam throng-h a pivotal connectionwith the upper end of linkage member 36.

In addition to the above described thermostatic arrangement, a vacuum orpressure responsive motor assembly 50 is provided and operativelyconnected to the choke valve 38 for causing an intial opening of thechoke valve 38, against the force of thermostatic spring 42, wheneverthe engine is started cold.

FIG. 3 illustrates, in enlarged cross-section, a fragmentary portion ofthe carburetor 10 in combination with the vacuum responsive motorassembly 50 which is shown in axial cross-section.

As illustrated in FIG. 3, the housing 52 of assembly 50 may be comprisedof first and second housing portions 54 and 56 which are suitablyretained in assembled relationship so as to peripherally retaintherebetween a pressure responsive diaphragm 58. If desired, suitableannular seals 60 and 62 may be disposed on opposite sides of thediaphragm 58 so as not to have the housing portions directly contact thediaphragm. Housing section 54 may in fact, as illustrated, be formedintegrally with carburetor body 12 by having an extending portiondefining an opening therein for the reception of certain of the elementsof the pressure responsive assembly 50.

The diaphragm or pressure responsive member 58 in effect defines twovariable but distinct chambers 64 and 66 of which chamber 64 is ventedto a source of relatively high pressure. In this case, such venting orcommunication is accomplished by means of an aperture or conduit means68 in communication with a source of atmospheric pressure as may existabove the choke valve 38 and below the air cleaner commonly associatedwith the carburetor 10 and fragmentarily illustrated at 70.

Cup-like reinforcing and clamping members 72 and 74 disposed on oppositesides of diaphragm 58 are retained thereagainst by means of a mountingstem 76, which includes an integrally formed flange portion 78 and afirst threaded shank portion 80, and a washerlike retainer 82. Nut 84threadably engaged with shank portion is effective for maintaining thewasher 82, cups 72 and 74, and diaphragm 58 in assembled relationshipagainst flange 78.

The left-most end of stem 76 is provided with an extension 86 which ispivotally connected, by means of a pivot pin 88, to one end 89 of a lostmotion connecting linkage 90 which has, at its other end, an elongatedslot 92 formed therein. A lever arm 94 operatively connected to orcarried at one end by choke valve 38 is connected at its other end tolinkage 90 by means of a pivot pin 96 which is carried by lever arm 94and slidably retained within slot 92. As shown, the connecting link 90may actually freely pass through the aperture 68 formed backing cup 74.Rotation of nut 102 will, in view of the above, evidently vary thepreload force of the compression spring 108.

Finally, an adjustable stop member is threadably engaged with housingsection 56 and positioned so as to be at times in axially abuttingengagement with the face 112 of spring perch or abutment 106.Preferably, stop member 110 is provided with an annular or O ring typeseal 114 for preventing leakage between chamber '66 and the ambientatmosphere. A tool-engaging surface is preferably provided as at 116 bywhich stop member 110 can be rotated in order to achieve axialadjustment thereof. A chamber-like opening 118 is formed at the left endof stop member 110 in order to accommodate the end of stem 76 as well asnut 102, as when surface 112 of spring abutment 106' is in abuttingengagement with end 120 of stop member 110, for example.-

A second axially adjustable stop member 126, which may be threadablycarried centrally of the stop 110, is also provided with an O ring typeseal 128 and a toolengaging slot by which axial adjustment of stop 126relative to stop member 110 can be achieved.

While, as previously stated, chamber 64 is in communication with asource of relatively high pressure, chamber 66 is in communication witha source of relatively low pressure as by conduit means 122 leading toport 124 formed in the carburetor 10 so as to be in communication withthe induction passage 14 at a location adjacent (slightly above and/orbelow) the throttle valve 18 when the throttle valve 18 is in itsabovementioned nominally closed position.

OPERATION The general operation of the invention is as follows. Forpurposes of illustration, let it first be assumed that the engine iscold and not running. At this time, the throttle valve 18 will be in itsshown nominally closed position and thermostatic element 42 will haveclosed the choke valve 38 moving it to the position shown in either ofFIGS. 1 or 2. Typically, at this time, the lip of throttle valve 18 isso situated with respect to port 124 (as also illustrated in FIG. 4) asto present some degree of communication between port 124 and theinduction passage 14 on the upstream side of the throttle valve 18, anda lesser degree of communication between the port 124 and the inductionpassage 14 on the engine side of the throttle valve 18. Depending uponthe particular engine requirement, the degrees of communication of port124 below and above the throttle valve 18 could be varied or reversed.

Now with the engine and thermostat 42 still cold, let it be assumed thatthe engine is started and running. At this time manifold vacuum existingbelow or posterior to the throttle valve 18 is communicated via port 124through conduit means 122 to chamber 66 of the vacuum responsive motorassembly 50. It should be evident that in the embodiment disclosed, thevalue of the vacuum communicated to chamber 66 will be somewhat lessthan the actual value of the manifold vacuum generated by the enginebecause of the slight bleed effect created by the port 124 communicatingto some degree with the induction passage 14 upstream of the throttlevalve 18.

Consequently, at this time the vacuum in chamber 66 is sufficient tomake the diaphragm 58 move to the right (as viewed in FIG. 2), againstthe resistance of thermostatic element 42, .until end face 112 of springseat 106 abuts against end 120 of the first stop or abutment member 110.Such movement of diaphragm 58, of course, causes a like movement of stemassembly 76 thereby moving the connecting linkage 90 to the right andcausing the choke valve 38 to be moved to a first partly opened orqualifying position as fragmentariily illustrated in phantom line at38a. If the engine and throttle valve 18 remain at the above describedconditions, the diaphragm 58 will not move any further to the rightbecause of the preloaded force in compression spring 108.

However, if it is assumed that the vehicle is driven away, under forexample part throttle operation, while the engine is still cold, it canbe seen that the throttle valve 18 is rotated some degreecounterclockwise (as viewed in FIGS. 1 and 4) thereby causing the portor slot 124 to either experience a further reduction in the degree ofpermissible communication with the induction passage upstream of thethrottle valve 18 or to have such communication completely terminated.Assuming that the throttle valve 18 has been sufficiently rotated as toplace the lower surface 132 thereof above the top of the slot or port124, it can be seen that the full manifold vacuum generated by theengine is applied directly through port 124 and conduit means 122 tochamber 66.

As a consequence of such full manifold vacuum being applied to chamber66, the pressure differential thusly created across diaphragm 58 issufficient to overcome the preloaded force of spring 108 causing thediaphragm 58 to compress spring 108 and thereby move stem assembly 76further to the right. Such movement of diaphragm 58 and stem assembly 76will continue until the right end of stem 76 approaches or actuallyabuts against the second adjustable stop or abutment member 126.Connecting linkage 90 will have been correspondingly moved causing thechoke valve 38 to move from the first partly open position 38a to asecond more nearly fully opened position as illustrated fragmentarily inphantom line at 38b. Such additional movement of the choke valve to aposition as at 38b serves to have the effect of leaning out the fuel-airratio of the combustible mixture being supplied to the engine.

The provision of adjustable stops 110 and 126 along with the adjustmentnut 102 enables the adjustment of the preload force in spring 108 aswell as the adjustment of the positions to which the choke valve willinitially move both upon starting of the engine and during cold enginedrive away.

FIG. 2, in which all elements which are like or similar to those of FIG.3 are identified with like reference numbers, illustrates a secondembodiment of the invention as comprising a housing 140 having formedtherein a cylindrical chamber 142 for the slidable reception therein ofa piston assembly 144. The piston assembly 144, is, in turn, comprisedof a first piston member 146, in sliding engagement with the wall ofchamber 142, operatively connected, as by a pivot -148, to end 89 of theconnecting linkage 90 (as also shown in FIG. 3). A stem-like extensionportion 150 carried by piston 146 passes through an aperture 152 formedin end 154 of a second piston member 156 serves to connect both pistons146 and 156 together. An end stop portion 158, which may be adjustablein a manner similar to nut 102 (in FIG. 3), formed on or carried bystern 150 serves to prevent separation of the pistons 146 and 156 whilea compression spring 160, generally contained between pistons 146 and156 serves to resiliently urge the pistons away from each other andthereby resiliently maintain piston 156 against the end stop 158.

A first threadably adjustable stop member 162 passing through a wall ofthe housing 140 has a contoured tip 164 which, as illustrated, is placedin the path of travel of piston 156 so that abutting engagement will beachieved therebetween whenever the engine is initially started. Itshould be apparent that as adjustable stop 162 is withdrawn that pistonassembly 144 will travel further to the right before abutting againstthe contoured tip 164. Of course, the vacuum is communicated to end 166of chamber 142 via conduit means 122 and port or slot 124 as in theembodiment of FIG. 3.

With the elements in the positions shown in FIG. 2, the choke valve 38would assume a position as shown at 38a of FIG. 2. That is the abuttingof piston 156 against stop 162 would be equivalent to the spring seat106 of FIG. 3 being in abutting engagement with end of I stop 110. Also,as throttle valve 18 was opened to a part throttle condition theincreased vacuum supplied to end 166 would be transmitted through one ora plurality of passages 168, formed in end 154 of piston 156, to thespace between the pistons 156 and 146 and thereby create a pressuredifferential across piston 146 sufficient to overcome the preload forceof spring 160. Consequently, piston 146 would move to the right untilthe end 158 of stem abuts against the second adjustable stop member 126.As in the case of member 100, however, a stable condition could resultwhere end 158 is not positioned against stop 126. Such movement of thepiston 146 would cause connecting linkage 90 to move the choke valve 38to a position corresponding to 38b of FIG. 3.

In view of the preceding, it can be seen that the invention providesmeans for modulating the choke position, during cold engine operation,in accordance with throttle valve position. This is accomplished throughthe use of a timed vacuum pick-up port means; that is, by timed it ismeant that the porting means is brought progressively further into fullcommunication with a source of manifold vacuum as the throttle valve ismoved from its nominally closed position to a part throttle position. Inconjunction with this, pressure responsive means are provided so as tobe acted upon by the manifold vacuum in order to establish a firstpartly opened position of the choke valve whenever the engine is coldand running with the throttle valve in a nominally closed position, anda second partly opened position, more nearly fully open than the firstposition, whenever the throttle is moved from its nominally closedposition toward a part throttle position. In this respect it can be seenthat the porting means 124 and the edge of the throttle valve 18 combineto form a valving means or mechanism by which a tailored or regulateddegree of vacuum communication is permitted with the pressure responsiveassembly such as 50.

By means such as above, the invention enables the fuelair ratio to besufliciently rich during curb idle cold engine operating conditions andstill to some degree lean-out the fuel-air ratio of the combustiblemixture when the cold engine has to operate at driving conditions.

As a consequence of the above, the degree of unburned hydrocarbonexhaust emission usually experienced with the prior art arrangements isreduced, fuel economy is increased and significantly smoother engineoperation is achieved especially in the drive-away condition.

It should also be made clear that various configurations and positionsof Vacuum porting means could be employed in place of porting means 124.As one further example, porting means 124 could be replaced by a seriesof generally vertically spaced small cross-sectional passages or portseach interconnected to the others and ultimately connected to conduitmeans 122, much in the manner as sometimes employed for controlling theadvance mechanism of a pressure actuated ignition distributor assembly.Any such arrangement may, of course, be employed without departing fromthe spirit of the invention. Further, it should be apparent that sincethe porting means 124 and the edge of throttle valve 18 form a valvingmeans, that other forms of valving means could be employed forperforming the desired function. For example, the throttle shaft 20could be formed to either form a portion of a suitable valving mechanismor to control a re lated valving mechanism which would in turn beeffective for varying the manifold vacuum in the pressure responsivemotor means in accordance with throttle valve position.

Although basically only two embodiments of the invention have beendisclosed and described, it should be apparent that other embodimentsand modifications of the invention are possible in View of the teachingsherein disclosed.

I claim:

1. In a carburetor for internal combustion engines, a

throttle valve, a choke valve, means including a heat responsive deviceto close said choke valve at low temperatures, a device responsive toengine vacuum for causing at least a partial opening of said choke valveagainst the tension of said heat responsive device upon starting of theengine, and abutment means adapted to limit the amount of choke openingdue to said engine vacuum responsive device, said abutment meansincluding a first portion eifective for establishing a first maximumpartly open choke valve position when said engine is operating with saidthrottle valve in a closed throttle position, and a second portioneffective for establishing a second maximum partly open choke valveposition more nearly fully opened than said first partly open chokevalve position when said throttle valve is moved away from said closedthrottle position...

2. A carburetor according to claim 1 wherein said vacuum responsivedevice comprises a pressure responsive, movable wall member, saidcarburetor further including connecting means operativelyinterconnecting said choke valve and said movable wall member, saidfirst portion including first stop means operatively engaged by saidwall member upon application of a first pressure differential acrosssaid wall member, and said second portion including second stop meansspaced from said first abutment means, said second stop means beingoperatively engaged by said wall member upon application of a secondpredetermined pressure differential greater than said first pressuredifferential across said wall member.

3. A carburetor according to claim 1, wherein said abutment means isconstructed so that said second choke position is variable up to itsmaximum partly open position, depending upon the vacuum applied to saiddevice.

4. A carburetor according to claim 1 wherein said vacuum responsivemeans comprises a movable pressure responsive member operativelyconnected to said choke valve, said carburetor further including valvingmeans for variably applying said engine vacuum to one side of saidmovable member, said first portion including first stop means for attimes operatively engaging said movable member in order to therebyestablish said first partly opened choke position, and said secondportion including second stop means for at times operatively engagingsaid movable member in order to thereby establish said second morenearly fully opened choke position.

5. A carburetor according to claim 4, wherein at least one of said stopmembers is provided with means for adjustment thereof.

6. A carburetor according to claim 1 wherein said temperature responsivemeans normally resists opening movement of said choke valve when saidengine is cold, wherein said pressure responsive device comprises ahousing defining a general chamber therein, a pressure responsivemovable wall member contained within said general chamber and definingat opposite sides first and second variable but distinct pressurechambers, said first pressure chamber being in communication with asource of relatively high pressure, conduit means effective forcompleting communication between said source of engine vacuum and saidsecond pressure chamber, said first portion including a first stopmember and a first abutment member operatively carried by said pressureresponsive movable wall member, means resiliently urging said firstabutment member away from said wall member, and said second portionincluding a second stop member and a second abutment member operativelycarried by said pressure responsive wall member, said first stop memberand said first abutment member being effective to engage each other uponthe admission of a first value of engine vacuum to said second pressurechamber thereby arresting further 8 movement of said wall member, andsaid wall member being further effective upon admission of a secondvalue of engine vacuum greater than said first value to move against theresistance of said resilient means until such time as said secondabutment member engages said second stop member.

7. A carburetor according to claim 6 wherein said conduit meansterminates in porting means formed in and communicating with saidinduction passage, said porting means comprising at least one aperturepositioned so as to be partly closed to communication with said sourceof engine vacuum by said throttle valve when said throttle valve is inits closed position.

8. A carburetor according to claim 6 wherein said conduit meansterminates in porting means formed in and communicating with saidinduction passage, said porting means being so positioned as to bepartly exposed to the source of engine vacuum downstream of the throttlevalve when said throttle valve is in its closed position andsimultaneously partly exposed to the atmospheric pressure upstream ofsaid closed throttle valve.

9. A carburetor according to claim 6 wherein said pressure responsivemovable wall member comprises a pressure responsive diaphragm, whereinsaid first abutment member comprises a movable spring seat, and whereinsaid resilient means comprises a compression spring contained generallybetween said diaphragm and said spring seat.

10. A carburetor according to claim 6 wherein said pressure responsivemovable wall member comprises a pressure responsive piston, wherein saidfirst abutment member comprises a spring seat, and wherein saidresilient means comprises a compression spring contained generallybetween said piston and said spring seat.

11. A carburetor according to claim 6 wherein said pressure resonsivemovable wall member comprises a pressure responsive diaphragm assembly,a stem portion carried by said diaphragm assembly and extendinggenerally axially thereof, wherein said first abutment member comprisesa movable spring seat slidably situated on and retained by said stemportion, wherein said resilient means comprises a compression springcontained generally between said diaphragm assembly and said springseat, including adjustment means carried by said stem portion foradjusting the preload force of said compression spring, wherein saidfirst stop member comprises a threadably adjustable stop carried by saidhousing and generally extending into said second pressure chamber, andwherein said second stop member comprises a threadably adjustable secondstop also operatively carried by said housing in a manner so as to havean end thereof generally within said second pressure chamber.

12. A carburetor according to claim 6, wherein means are provided toadjust the preload of said resilient means.

References Cited UNITED STATES PATENTS 787,480 4/1905 Tanner 92-65X'2,506,374 5/1950 McMahon 92-65X 2,988,344 6/ 1961 Smitley 261-39(.2)3,159,692 12/1964 Kittler 261-39(.2) 3,171,868 3/1965 Hamilton 26139(.2)3,187,640 6/1965 Young et a1. 92-65X 3,279,771 10/ 1966 Herman et al.26139(.2) 3,321,194 5/1967 Oarlson 26l39(.2)

TIM R. MILES, Primary Examiner U.S. Cl. X.R, 926 5

